1. Field of the Invention
This invention relates to new chemical compositions and to lubricating oil compositions containing these compositions. More particularly, it relates to a novel class of chemical compositions which act as rust and corrosion inhibitors in lubricating oils.
2. Description of the Prior Art
The prior art has taught the need for efficient rust inhibitors in lubricating oils. The need is particularly prevalent in engines which are infrequently operated or which are subject to extended storage in humid climates, because these engines experience excessive rusting of cylinder walls, wrist pins and other polished working surfaces. Under such conditions, moisture accumulates within the engine, penetrates the lubricating film and attacks ferrous surfaces. This attack is aggravated by residues of chlorine and bromine compounds produced in the combustion of gasolines containing tetraethyl lead and scavenging agents such as ethylene dibromide.
The prior art has also recognized the need for efficient corrosion inhibitors in gasoline to prevent or reduce the deposition of lacquer or varnish-like coatings on the walls of cylinders, piston rings, etc., and to prevent or reduce the corrosion of engine parts, bearings, etc. Such corrosion inhibitors, for example, prevent copper-lead bearing corrosion.
Certain alkyl and alkenyl dicarboxylic anhydrides, acids, and various salts thereof have been proposed as ashless or low ash rust inhibitors for motor lubricants. In ashless or low ash formulations, however, these anhydrides and acids can cause considerable copper-lead bearing weight loss. The prior art has generally taught that when using a salt of a hydrocarbon-substituted dicarboxylic acid, the size of the hydrocarbon substituent of the dicarboxylic compound appears to determine the effectiveness of the additive in lubricating oils. Thus, the prior art is replete with statements to the effect that it is critically important that the substituent be large; that is, that it have at least about 50 aliphatic carbon atoms in its structure and the molecular weight of the hydrocarbon substituent should be with the range of about 700 to about 10,000. Because such salts have high molecular weight hydrocarbon substituents, a relatively high weight per cent active ingredient of salts is required in the oil. The shorter chain aliphatic-hydrocarbon-substituted dicarboxylic anhydrides and acids, and their salts, while having rust inhibiting properties, are generally insoluble in oil, and thus present special problems to their successful incorporation as rust inhibitors in lubricating compositions. The rust inhibitors also must be compatible with other additives conventionally used in motor lubricants and sometimes this has also proved to be a problem.
Accordingly, there has been a continuing search for new and improved, economical, low ash rust inhibitors which are compatible with other lubricating oil additives and do not cause significant corrosion.